Storage element and memory

ABSTRACT

A storage element includes a magnetization fixed layer, and a magnetization free layer. The magnetization fixed layer includes a plurality of ferromagnetic layers laminated together with a coupling layer formed between each pair of adjacent ferromagnetic layers. The magnetization directions of the ferromagnetic layers are inclined with respect to a magnetization direction of the magnetization fixed layer.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a national stage of International ApplicationNo. PCT/JP2012/007416 filed on Nov. 19, 2012 and claims priority toJapanese Patent Application No. 2011-2618523 filed on Nov. 30, 2011, thedisclosure of which is incorporated herein by reference.

BACKGROUND

The present technology relates to a storage element and a memory whichhave a plurality of magnetic layers and perform recording while using aspin torque magnetization reversal.

Various types of information devices such as a mobile terminal and amass storage server have made rapid progress. Therefore, memories andelements such as logic elements composing these devices have beenexpected to have higher performance such as high integration, high speedprocessing and low consumed power. Particularly, nonvolatilesemiconductor memories have considerably made progress, and a flashmemory acting as a mass storage file memory has been diffused so as toexpel a hard disc drive. In contrast, a ferroelectric random accessmemory (FeRAM), a magnetic random access memory (MRAM), a phase-changerandom access memory (PCRAM) and the like have been developed so as tobe used in place of a NOR flash memory, a dynamic random access memory(DRAM) and the like generally used now, while being considered to beused for a code storage and further to be developed as a working memory.A part of these developed RAMs have been already put to practical use.

The MRAM among these RAMs performs data recording based on themagnetization direction of a magnetic substance so as to be rewritablesubstantially limitless times (10¹⁵ times or more) at high speed.Therefore, the MRAM has been already used in fields of industrialautomation, aircrafts and the like. Because of high speed operation andreliability of the MRAM, it is expected that the MRAM is developed as acode storage or a working memory. However, the MRAM has problems inactual use in view of low consumed power and large storage capacity.These problems result from a recording principle of the MRAM, that is, arecording method in which the magnetization direction is reversed by amagnetic field induced by an electric current of a wire.

As one of methods for solving these problems, recording not depending onthe magnetic field of the current, that is, a magnetization reversingmethod has been examined. Especially, the spin torque magnetizationreversal has been actively researched (e.g., refer to Patent Literatures(PTL) 1 and 2).

In the same manner as the MRAM, a storage element using the spin torquemagnetization reversal is often structured by a magnetic tunnel junction(MTJ) and a tunneling magnetoresistive (TMR) element. In this structure,the phenomenon that a spin polarized electron passing through a magneticlayer of which magnetization is fixed in a direction gives a torque toanother free magnetic layer (of which magnetization is not fixed) whenentering this free magnetic layer (also called spin transfer torque) isutilized. When a current having a value equal to or more than athreshold value flog the magnetization direction of this free magneticlayer is reversed. The rewriting of 0 and 1 is performed by changing thepolarity of the current.

The absolute value of the current for the reversal of the magnetizationis equal to or less than 1 mA when the storage element has the size ofapproximately 0.1 μm Further, because this current value is decreasedwith the element volume, the size adjustment is possible. Moreover,because no word wire to induce the magnetic field of current forrecording in the MRAM is used, there is a merit that the cell structureis simplified.

Hereinafter, the MRAM using the spin torque magnetization reversal iscalled a spin torque magnetic random access memory (ST-MRAM). The spintorque magnetization reversal is also called a spin injectionmagnetization reversal. This ST-MRAM is greatly expected as anonvolatile memory in which low consumed power and large storagecapacity are possible while the merits of the MRAM being operated athigh speed and being rewritable substantially limitless time maintained.

CITATION LIST Patent Literature

[PTL 1]

-   Japanese Patent Application Laid-open No. 2003-17782    [PTL 2]-   U.S. Pat. No. 5,695,864

SUMMARY

However, the strength of the spin torque causing the magnetizationreversal in the ST-MRAM is changed with the magnetization direction. Inthe structure of the storage element having the normal ST-MRAM, amagnetization angle at which the spin torque is equal to zero exists.

When a magnetization angle in the ST-MRAM set in an initial stateaccords with this magnetization angle, the time necessary for themagnetization reversal is considerably lengthened. Therefore, themagnetization reversal is sometimes not completed within a writingperiod of time.

When the reversal is not completed within a writing period of time, thiswriting operation is failed (writing error), and no normal writingoperation can be performed.

In view of the circumstances as described above, it is desirable toprovide a storage element and a memory which are capable of performing awriting operation in a short time without causing any writing error.

In an embodiment, a storage element includes a magnetization fixedlayer, and a magnetization free layer. The magnetization fixed layerincludes a plurality of ferromagnetic layers laminated together with acoupling layer formed between each pair of adjacent ferromagneticlayers. The magnetization directions of the ferromagnetic layers areinclined with respect to a magnetization direction of the magnetizationfixed layer.

In another embodiment, a method of writing information to a storageelement including a magnetization fixed layer, and a magnetization freelayer including a plurality of ferromagnetic layers laminated togetherwith a coupling layer formed between each pair of adjacent ferromagneticlayers is provided. The method includes applying a current in amagnetization direction of the magnetization fixed layer to cause a spintorque magnetization reversal in the magnetization free layer. Themagnetization directions of the ferromagnetic layers are inclined withrespect to the magnetization direction of the magnetization fixed layer.

In another embodiment, a spin torque magnetic random access memoryelement includes a magnetization fixed layer having a fixedmagnetization in a perpendicular direction relative to a film surface ofthe magnetization fixed layer, a magnetization free layer including aplurality of ferromagnetic layers laminated together with a couplinglayer formed between each pair of adjacent ferromagnetic layers, therebymagnetically coupling the ferromagnetic layers, and a nonmagnetic layerformed between the magnetization fixed layer and the magnetization freelayer. The magnetization directions of the ferromagnetic layers areinclined with respect to the perpendicular direction.

In another embodiment, a magnetoresistive effect type magnetic headincludes a first magnetic shield formed on a substrate via an insulatinglayer; a magnetic sensing element including a magnetization fixed layer,and a magnetization free layer including a plurality of ferromagneticlayers laminated together with a coupling layer formed between each pairof adjacent ferromagnetic layers, and a second magnetic shield formed onthe magnetic sensing element via the insulating layer. The magnetizationdirections of the ferromagnetic layers are inclined with respect to amagnetization direction of the magnetization fixed layer.

In the storage element according to the first embodiment of the presenttechnology, although a period of time necessary for the magnetizationreversal is dispersed when the directions of the magnetizations of boththe storage layer and the magnetization fixed layer become approximatelyparallel or antiparallel to each other, this dispersion may besuppressed by the magnetic coupling between the ferromagnetic layerscomposing the storage layer. Therefore, the writing of information maybe performed by reversing the direction of the magnetization of thestorage layer within a predetermined finite period of time.

Further, the value of the writing current used to reverse the directionof the magnetization of the storage layer may be reduced.

Moreover, because of strong anisotropic magnetic energy held in theperpendicular magnetization film, the thermal stability of the storagelayer may be sufficiently maintained.

Further, in the memory according to the second embodiment of the presenttechnology, a current flows through the storage element in thelamination direction via the two types of wires, and spin transferoccurs. Therefore, by a current flowing through the storage element inthe lamination direction via the two types of wires, the recording ofinformation based on the spin torque magnetization reversal may beperformed.

Further, because the thermal stability of the storage element may besufficiently maintained, information recorded in the storage element maybe stably held, and the downsizing, the improvement of reliability andlow consumed power in the memory may be achieved.

As described above, according to the present technology, because thewriting of information while reversing the direction of themagnetization of the storage layer within a predetermined period of timemay be performed, the writing error may be reduced, and the writingoperation may be performed in a shorter time.

Further, because the writing error may be reduced, the reliability inthe writing operation may be improved. Moreover, because the writingoperation may be performed in a shorter time, the operation speed may beheightened.

Accordingly, the memory having the high reliability in the writingoperation and being operated at high speed may be achieved according tothe present technology.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

[FIG. 1]

FIG. 1 is a schematic perspective view of a memory according to anembodiment of the present technology.

[FIG. 2]

FIG. 2 is a cross-sectional view of the memory according to theembodiment.

[FIG. 3]

FIG. 3 is a plan view of the memo according to the embodiment.

[FIG. 4]

FIG. 4 is a schematic structural view (cross-sectional view) of astorage element having a storage layer which includes a magneticsubstance magnetized in the direction perpendicular to a film surface.

[FIG. 5]

FIG. 5 is a schematic structural view (cross-sectional view) of thestorage element according to the embodiment.

[FIG. 6A]

FIG. 6A is a schematic structural view (perspective view) of the storagelayer according to the embodiment.

[FIG. 6B]

FIG. 6B is a schematic structural view (top view) of the storage layeraccording to the embodiment.

[FIG. 7]

FIG. 7 is a diagram in which a range of magnetic-coupling energy isplotted.

[FIG. 8]

FIG. 8 is a diagram in which a relation between the magnetic-couplingenergy and an index of thermal stability is plotted.

[FIG. 9]

FIG. 9 is a diagram in which a range of magnetic energy is plotted.

[FIG. 10]

FIG. 10 is a diagram in which a relation between excitation energy and areversal time is plotted.

[FIG. 11A]

FIG. 11A is an explanatory perspective view of a magnetic head to whichthe embodiment is applied.

[FIG. 11B]

FIG. 11B is an explanatory cross-sectional view of the magnetic head.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present technology will be describedin the following order.

<1. Schematic Structure of Memory According To This Embodiment>

<2. Overview of Storage Element According to This Embodiment>

<3. Concrete Structure according to This Embodiment>

<4. Modification>

<1. Schematic Structure of Memory According to this Embodiment>

Initially, a schematic structure of a memory will be described.Schematic views of a memory are shown in FIG. 1, FIG. 2 and FIG. 3. FIG.1 is a perspective view, FIG. 2 is a sectional view, and FIG. 3 is aplan view.

As shown in FIG. 1, in the memory, a storage element 3 having a ST-MRAMis located near each of cross-over points of two types of address wires(e.g., word lines and bit lines) extending perpendicular to each other.The ST-MRAM is capable of holding information indicated by a magneticstate. More specifically, a drain region 8, a source region 7, and agate electrode 1 that constitute a selecting transistor for selectingeach of memory cells are formed in a portion separated by elementseparating layers 2 of a semiconductor body 10 such as a siliconsubstrate. The gate electrode 1 also acts as one address wire (the wordline) extending in the front-back direction in FIG. 1.

The drain region 8 is formed in common to two selecting transistorslocated on right and left sides in FIG. 1. A wire 9 is connected to thisdrain region 8. The storage element 3 having a storage layer is locatedbetween the source region 7 and a bit line 6 being located on an upperside and extending in the lateral direction in FIG. 1. The direction ofthe magnetization of the storage layer is reversed by a spin torquemagnetization reversal. The storage element 3 is, for example, formed ofa magnetic tunnel junction element (a MTJ element).

As shown in FIG. 2, the storage element 3 has two magnetic layers 12 and14. One of these magnetic layers 12 and 14 is a magnetization fixedlayer 12 in which the direction of magnetization M12 is fixed, and theother magnetic layer is a storage layer 14, that is, a free magnetizedlayer in which the direction of magnetization M14 is changeable.

Further, the storage element 3 is connected to the bit line 6 and thesource region 7 via respective upper and lower contact layers 4.

Therefore, when a current flows through the storage element 3 via twotypes of address wires 1 and 6 in the vertical direction, the directionof the magnetization M14 of the storage layer 14 may be reversed by aspin torque magnetization reversal.

As shown in FIG. 3, in the memory, a large number of first wires bitlines) 1 and a large number of second wires (e.g., word lines) 6 arearranged perpendicular to one another in the matrix shape, and thestorage elements 3 are located on cross-over points of the wires 1 and6.

Each storage element 3 is formed in a circular shape in the planethereof and has a cross-sectional structure shown in FIG. 2.

Further, as shown in FIG. 2, the storage element 3 has one magnetizationfixed layer 12 and one storage layer (free magnetized layer) 14.

Each storage element 3 forms one of memory cells of the memory.

In the memory described above, it is necessary to perform a writingoperation by a current having an amount equal to or lower than asaturation current of the selecting transistor. It is well known thatthe saturation current of the transistor is decreased with downsizing ofthe transistor. Therefore, to downsize the memory, it is desirable thatthe efficiency in spin transfer be improved to reduce the currentflowing through the storage element 3.

Further, to increase the level of a read-out signal, a large magneticresistance changing rate should be secured. Therefore, it is effectiveto adopt the MTJ structure as described above. More specifically, it iseffective that the storage element 3 has an intermediate layer being atunnel insulating layer (a tunnel barrier layer) between the magneticlayers 12 and 14.

When the tunnel insulating layer is used as the intermediate layer asdescribed above, the amount of the current flowing through the storageelement 3 is restricted to prevent the tunnel insulating layer fromreceiving dielectric breakdown. That is, in view of securing thereliability in the repeated writing to the storage element 3, it isdesirable that a current necessary for the spin torque magnetizationreversal be suppressed. The current necessary for the spin torquemagnetization reversal is sometimes called a reversing current or astoring current.

Further, because the memory is a nonvolatile memory, it is necessary tostably store information written by the current in other words, it isnecessary to secure stability (thermal stability) to thermal fluctuationof the magnetization of the storage layer.

Assuming that the thermal stability of the storage layer is not secured,the direction of the reversed magnetization is sometimes reversed againdue to heat (temperature in operation circumstances), and a holdingerror is undesirably caused.

As compared with the past MRAM, the storage element (ST-MRAM) 3 in thismemory has the advantage of sizing. That is, it is possible to reducethe volume of the element 3. However, the volume reduction causesdeterioration of the thermal stability if other characteristics are notchanged.

Because the increase in the storage capacity of ST-MRAM further reducesthe volume of the storage element 3, the securing of the thermalstability is important.

Therefore, the thermal stability in the storage element 3 of T-RAM is avery important characteristic, and it is desirable that the element 3 bedesigned so as to secure this thermal stability even if the volume ofthe element 3 is reduced.

<2. Overview of Storage Element According to this Embodiment>

Next, the abstract of the storage element according to this embodimentwill be described.

A schematic structural view (a cross-sectional view) of the storageelement of ST-MRAM in which the direction of magnetization isperpendicular to a film surface of the element is shown in FIG. 4.

As shown in FIG. 4, the storage element has the magnetization fixedlayer (also called a reference layer) 12, located on an underlayer 11,in which the direction of the magnetization M12 is fixed, anintermediate layer (a nonmagnetic layer) 13, the storage layer (the freemagnetized layer) 14 in which the direction of the magnetization M14 ischangeable, and a cap layer 15 that are laminated in that order.

In the layer 12 of these layers, the direction of the magnetization M12is fixed by a high coercive force and the like to be perpendicular to afilm surface of the layer 12.

In the storage element shown in FIG. 4, the storage of informationindicated by the direction of the magnetization (a magnetic moment) M14of the storage layer 14 having uniaxial anisotropy is performed.

The writing of information to the storage element is performed byapplying a current in the direction perpendicular to film surfaces ofthe layers of the storage element (i.e., the lamination direction of thelayers) to cause a spin torque magnetization reversal in the freemagnetized layer becoming the storage layer 14.

Here, the spin torque magnetization reversal will be described in brief.

An electron has one of two types of spin angular momentums, and theseare provisionary called an upper spin angular momentum and a lower spinangular momentum.

In the inside of a nonmagnetic substance, the number of electrons havingthe upper spin angular momentum is equal to the number of electronshaving the lower spin angular momentum. In the inside of a ferromagneticsubstance, these numbers differ from each other.

Initially, the case where, when the directions of the magnetizations M12and M14 are antiparallel to each other in two ferromagnetic substancelayers (the magnetization fixed layer 12 and the free magnetized layer14) laminated each other via the intermediate layer (the nonmagneticlayer) 13, electrons are moved from the magnetization fixed layer 12 tothe storage layer (the free magnetized layer) 14 is considered.

Spins of electrons passing through the magnetization fixed layer 12 arepolarized. That is, the number of electrons having the upper spinangular momentum differs from the number of electrons having the lowerspin angular momentum.

When the thickness of the nonmagnetic layer 13 is sufficiently thin, theelectrons reach another magnetic substance, that is, the storage layer(the free magnetized layer) 14 before the spin polarization is lightenedso as to be set in the non-polarized state (the number of electronshaving the upper spin angular momentum is equal to the number ofelectrons having the lower spin angular momentum) of a normal nonenonmagnetic substance.

Then, because signs of spin polarization level in two ferromagneticsubstance layers (the magnetization fixed layer 12 and the freemagnetized layer 14) differ from each other, the spin in a part of theelectrons is reversed to reduce energy in this system. That is, thedirection of the spin angular momentum is changed. At this time, becausethe whole angular momentum in the system should be conserved, a reactionequivalent to the sum of changes in the angular momentum caused by theelectrons, of which the spin direction is changed, is given to themagnetization M14 of the storage layer (the free magnetized layer) 14.

When the amount of the current, that is, the number of electrons passingper unit time is small, the number of electrons of which the spindirection is changed is also small. Therefore, a change in the angularmomentum caused in the magnetization M14 of the storage layer (the freemagnetized layer) 14 is also small. In contrast, when the amount of thecurrent is increased, a large change in the angular momentum may begiven within one unit time.

The time change in the angular momentum is a torque. When this torqueexceeds a threshold value, the magnetization M14 of the storage layer(the five magnetized layer) 14 starts a precession and is stabilized dueto the uniaxial anisotropy of the storage layer (the free magnetizedlayer) 14 when the rotational axis is rotated by 180 degrees. In otherwords, the reversal from the antiparallel state to the parallel state iscaused.

In contrast, when a current flows inversely so as to send electrons fromthe storage layer (the free magnetized layer) 14 to the magnetizationfixed layer 12 in the case where the directions of the magnetizationsM12 and M14 of the two ferromagnetic substance layers 12 and 14 areparallel to each other, electrons are reflected by the magnetizationfixed layer 12.

Then, when the electrons reflected so as to reverse the spin directionof the electrons enter the free magnetized layer 14, the electrons givea torque so as to reverse the direction of the magnetization M14 of thestorage layer (the free magnetized layer) 14. Therefore, themagnetizations M12 and M14 may be changed to the antiparallel state.

In this case, the current amount necessary to cause this reversalbecomes larger than the current amount necessary to cause the changefrom the antiparallel state to the parallel state.

It is difficult to intuitively recognize the change from the parallelstate to the antiparallel state. However, it may be thought that thedirection of the magnetization M12 of the magnetization fixed layer 12is difficult to be reversed because the magnetization M12 is fixed, butthe direction of the magnetization M14 of the free magnet zed layer 14is reversed to conserve the angular momentum of the whole system.

As described above, the recording of information being each of 0 and 1is performed by a current flowing in one direction from themagnetization fixed layer (reference layer) 12 to the storage layer (thefree magnetized layer) 14 or in the opposite direction at a value equalto or higher than a threshold value corresponding to the polarity of thecurrent.

The reading-out of the information is performed by using themagnetoresistive effect in the same manner as in the past MRAM.

More specifically, in the same manner as the case of the informationrecording described above, a current flows in the directionperpendicular to the film surface of each layer (the laminationdirection of each layer). Then, because the electric resistanceindicated by the storage element when the direct on of the magnetizationM14 of the storage layer (the free magnetized layer) 14 is parallel tothe direction of the magnetization M12 of the magnetization fixed layer(reference layer) 12 differs from the electric resistance when thedirection of the magnetization M14 is antiparallel to the direction ofthe magnetization M12, this phenomenon is utilized.

The material used for the intermediate layer nonmagnetic layer) 13 maybe metal or insulator. However, when insulator is used for thenonmagnetic layer 13, a read-out signal of a higher level (a higherchange rate of resistance) may be obtained, and the recording using acurrent of a lower value may be performed. This element using theinsulator is called a magnetic tunnel junction (MTJ) element.

The strength of the spin torque described above changes with the anglebetween the magnetization M14 of the storage layer (the free magnetizedlayer) 14 and the magnetization M12 of the magnetization fixed layer(the reference layer) 12. When the unit vector indicating the directionof the magnetization M14 is expressed by m1 while the unit vectorindicating the direction of the magnetization M12 is expressed by m2,the strength of the spin torque is proportional to m1×(m1×m2). Here, “x”denotes the outer product of a vector.

The magnetization M12 of the magnetization fixed layer 12 is normallyfixed to the direction of easy magnetization axis of the storage layer14. The magnetization M14 of the storage layer 14 is apt to be directedto the easy magnetization axis direction of the storage layer 14 itself.At this time, the vectors m1 and m2 make an angle of 0 or 180 degrees.Therefore, no spin torque acts at all according to the spin torqueequation described above.

In the actual case, the magnetization M14 of the storage layer 14 isdistributed at random around the easy magnetization axis due to thermalfluctuation. When the direction of the magnetization M14 to thedirection of the magnetization M12 of the magnetization fixed layer 12goes away from the angle of 0 degree or 180 degrees, a spin torque acts,and the magnetization reversal may be caused.

A magnetic substance has magnetic energy of a strength corresponding tothe direction of magnetization thereof. The direction most reducing themagnetic energy is the easy magnetization axis. When no thermalfluctuation is caused, the magnetization is directed to the easymagnetization axis by a force (a torque) minimizing the magnetic energy.In contrast, when the magnetization direction is apart from the easymagnetization axis due to the thermal fluctuation, the magnetic energybecomes large as compared with the magnetic energy set when themagnetization is directed to the easy magnetization axis. Thisdifference is called excitation energy E. Then, when the magnetizationdirection further goes away from the easy magnetization axis such thatthe excitation energy E exceeds a certain threshold value, themagnetization reversal is caused. This threshold value is expressed byΔ. The threshold value Δ may be regarded as energy necessary to reversethe magnetization. Although the excitation energy E and the thresholdvalue Δ are expressed by the unit of joule (J), dimensionless quantitiesobtained by dividing these by thermal energy (a product of Boltzmann'sconstant and absolute temperature) are used hereinafter. In this case,because the threshold value Δ may be regarded as an index indicating thestability of the magnetization to the thermal energy, the thresholdvalue Δ is sometimes called an index of thermal stability.

When the excitation energy E of the magnetization M14 of the storagelayer 14 and the index Δ of thermal stability are used, a current Iapplied to the storage layer 14 and a time period (a reversal time)t_(s) necessary for a spin torque magnetization reversal caused by thecurrent I satisfy the following Equation 1.

$\frac{{\eta( {I - I_{c\; 0}} )}t_{s}}{e} = {( \frac{M_{s}V}{\mu_{B}} ){\ln( {\frac{\pi}{2}\sqrt{\frac{\Delta}{E}}} )}}$

Here, Ic0 denotes a threshold current necessary to cause a spin torquemagnetization reversal, η denotes a spin polarization rate of thecurrent I, e denotes an electric charge of electron, Ms denotes asaturation magnetization of the magnetization M14, V denotes a volume ofthe storage layer 14, and μ_(B) denotes the Bohr magneton.

The left side of the Equation 1 corresponds to the number of electronsinjected into the storage layer 14. The right side of the Equation 1corresponds to the number of electrons existing in the storage layer 14.The scale of these numbers is adjusted by the logarithm term. The valueof the excitation energy E corresponds to the magnetization direction atthe time the current is applied.

As found from this Equation 1, the reversal time is infinitely divergedwhile the excitation energy E approaches zero. As described above, whenno thermal fluctuation is caused, the magnetization M14 is directed tothe easy magnetization axis corresponding to the energy E of zero, andthe diversion of the reversal time is a problem.

Therefore, in this technology, to suppress the diversion of the reversaltime described above, the storage layer is configured to have at leasttwo or more ferromagnetic layers laminated via a coupling layer. The twoferromagnetic layers adjacent to each other are magnetically coupledwith each other via the coupling layer inserted between them.

In the structure of the memory according to the embodiment of thepresent technology described above, because the directions of themagnetizations of both the storage layer and the magnetization fixedlayer become approximately parallel or antiparallel to each other by themagnetic coupling between the ferromagnetic layers composing the storagelayer, the diversion of the time period necessary for the magnetizationreversal may be suppressed, and the writing of information performed byreversing the direction of the magnetization of the storage layer withina predetermined finite period of time may be possible.

<3. Concrete Structure According to this Embodiment>

Next, the embodiment according to the present technology will beconcretely described.

FIG. 5 is a schematic structural view (a cross-sectional view) of astorage element composing the memory according to the embodiment of thepresent technology.

A storage element 20 shown in FIG. 5 has a magnetization fixed layer(also called a reference layer) 22, located on an underlayer 21, inwhich the direction of a magnetization M22 is fixed, an intermediatelayer (a nonmagnetic layer) 23, a storage layer (a five magnetizedlayer) 24 in which the direction of magnetization is changeable, and acap layer 25 that are laminated in that order.

In the magnetization fixed layer 22, the magnetization M22 is fixed tobe directed to the direction perpendicular to a film surface of themagnetization fixed layer 22 (the upper direction in FIG. 5).

The structure described above is the same as the structure of ST-MRAMshown in FIG. 4.

An anti-ferromagnetic (not shown) formed of an anti-ferromagneticsubstance may be located between the underlayer 21 and the magnetizationfixed layer 22 to fix the direction of the magnetization M22 of themagnetization fixed layer 22.

Further, the storage element 20 according to this embodiment differsfrom the structure of MTJ of ST-MRAM shown in FIG. 4 in that the storagelayer 24 includes a multiplayer film in which a plurality offerromagnetic layers and a coupling layer are laminated on one another.In FIG. 5, the storage layer 24 includes a three-layer structure havinga ferromagnetic layer 24 a, a coupling layer 24 b, and a ferromagneticlayer 24 c that are located in that order.

A magnetization M1 of the ferromagnetic layer 24 a and a magnetizationM2 of the ferromagnetic layer 24 c are magnetically coupled with eachother via the coupling layer 24 b. As the material of the coupling layer24 b, nonmagnetic metals such as Ta and Ru may be used.

As the material of the intermediate layer (the nonmagnetic layer) 23located between the magnetization fixed layer 22 and the storage layer24, insulating materials (various oxides) for forming a tunnelinsulating film or nonmagnetic metals used for a layer located betweenmagnetic layers of a magnetoresistive effect element may be used.

When an insulating material is used as the material of this intermediatelayer (the nonmagnetic layer) 23 as described above, a read-out signalof a higher level (a higher change rate of resistance) may be obtained,and recording using a current of a lower value may be performed.

As materials of the magnetization fixed layer 22 and the storage layer24, various magnetic materials used for MTJ of the past ST-MRAM may beused.

For example, CoFe may be used for the magnetization fixed layer 22, andCoFeB may be used for the storage layer 24.

Further, materials of NiFe, TePt, CoPtTbFeCo, GdFeCo, CoPd, MnBi, MnGa,PtMnSb, and Co—Cr family may be used. Moreover, magnetic materials otherthan these materials may be used.

In the same manner as in the storage element 3 shown in FIG. 4, thereading-out of information is performed by using the magnetoresistiveeffect.

More specifically, in the same manner as the recording of informationdescribed above, a current flows in the direction perpendicular to thefilm surface of each layer (the lamination direction of each layer).Then, the phenomenon that the electric resistance indicated by thestorage element is changed with a relative angle between the directionof the magnetization M22 of the magnetization fixed layer 22 and thedirection of the magnetization M1 of the ferromagnetic layer 24 a isused.

The structure of the storage layer 24 is shown further in detail in aperspective view of FIG. 6A and a top view of FIG. 6B. The intermediatelayer 24 b is omitted in FIG. 6A and FIG. 6B for simplification. In thestorage element 20 according to this embodiment, the storage layer 24 isformed in a column shape. To describe the directions of themagnetizations M1 and M2, angles θ1, θ2, φ1 and φ2 are defined asfollows. A perpendicular axis 31 penetrating through the storage layer24 along the perpendicular direction is shown in the perspective view.The angle between the direction of the magnetization M1 and theperpendicular axis 31 is defined as θ1, and the angle between thedirection of the magnetization M2 and the perpendicular axis 31 isdefined as θ2. Further, a reference line 32 passing through the centerof the storage layers 24 a or 24 c is shown in the top view. Because thestorage layers 24 a and 24 c are commonly formed in a circular shape incross-section, the direction of the reference line 32 may be arbitrarilyselected. When the magnetizations M1 and M2 are respectively projectedonto the film surfaces of the storage layers 24 a and 24 c, the anglebetween the direction of the magnetization M1 and the reference line 32is defined as φ1, and the angle between the direction of themagnetization M2 and the reference line 32 is defined as φ2.

As described above, a magnetic substance has magnetic energy of astrength corresponding to the direction of the magnetization thereof. Todescribe the magnetic energy, the following values are defined. Theenergy difference obtained by subtracting a strength of the magneticenergy at the time the magnetization M1 is directed to the perpendiculardirection (θ1=0 degree) from a strength of the magnetic energy at thetime the magnetization M1 is directed to an in-surface direction (θ1=90degrees) is indicated by Δ1. Further, the energy difference obtained bysubtracting a strength of the magnetic energy at the time themagnetization M2 is directed to the perpendicular direction (θ2=0degree) from a strength of the magnetic energy at the time themagnetization M2 is directed to an in-surface direction (θ2=90 degrees)is indicated by Δ2. Moreover, the strength of the magnetic couplingenergy between the magnetizations M1 and M2 is indicated by Δex. Thedifferences Δ1 and Δ2, and the strength Δex are expressed by the unit ofjoule (J). However, in the same manner as the thermal energy E and theindex Δ of thermal stability described above, dimensionless quantitiesobtained by dividing the differences and strength by thermal energy (aproduct of Boltzmann's constant and absolute temperature) are used.

In this case, the magnetic energy ∈ of the storage layer 24 is expressedby the following Equation 2.∈=Δ₁ sin²θ₁+Δ₂ sin²θ₂−Δ_(ex)(cos θ₁ cos θ₂+sin θ₁ sin θ₂ cos(φ₁−φ₂))

The excitation energy E of the storage layer 24 is expressed by anequation E=∈−∈min. Here, ∈min denotes the minimum value of the magneticenergy ∈. In the same manner as the case of the storage layer 14 in FIG.4, when no thermal fluctuation is caused, the excitation energy Ebecomes zero. That is, the directions of the magnetizations M1 and M2are changed such that the magnetic energy ∈ becomes ∈min (this state iscalled an equilibrium state). In the case of the storage layer 14, therelative angle between the direction of the magnetization M14 of thestorage layer 14 and the direction of the magnetization M12 of themagnetization fixed layer 12 is 0 degree (parallel) or 180 degrees(antiparallel) when the excitation energy E reaches zero. Therefore,there is a problem that the reversal time is increased while no spintorque acts. However, the inventors of the present technology performedvarious examinations and realized that, when the excitation energy Ereached zero, the directions of the magnetizations M1 and M2 might makeangles other than 0 degree (parallel) or 180 degrees (antiparallel) tothe direction of the magnetization M22 of the magnetization fixed layer22 (the perpendicular axis). That is, the magnetizations M1 and M2 maybe inclined with respect to the magnetization M22. At this time, becausea finite spin torque acts, it may be expected that the increase of thereversal time is suppressed.

Here, while using the Equation 2, the inventors performed variousexaminations of a condition that the magnetizations M1 and M2 areinclined with respect to the magnetization M22. As a result, thecondition was found out as follows. The case where the strength Δex ofthe magnetic coupling energy between the magnetizations M1 and M2 isequal to zero and the magnetizations M1 and M2 are separately moved isconsidered. According to the definition, when the difference Δ1 ispositive, the easy magnetization axis of the magnetization M1 becomesperpendicular to the film surface of the ferromagnetic layer 24 a, andthe magnetization M1 in the equilibrium state is directed to thedirection perpendicular to the film surface. In contrast, when thedifference Δ1 is negative, the easy magnetization axis of themagnetization M1 is placed in the film surface, and the magnetization M1in the equilibrium state is directed to an in-surface direction in thefilm surface of the ferromagnetic layer 24 a. At this time, because theferromagnetic layer 24 a is isotropic with respect to the rotation aboutthe perpendicular axis, the value of φ1 is arbitrary. In the samemanner, when the difference Δ2 is positive, the easy magnetization axisof the magnetization M2 is perpendicular to the film surface, and themagnetization M2 in the equilibrium state is directed to the directionperpendicular to the film surface of the ferromagnetic layer 24 c. Incontrast, when the difference Δ2 is negative, the easy magnetizationaxis of the magnetization M2 is placed in the film surface of theferromagnetic layer 24 c, and the magnetization M2 in the equilibriumstate is directed to an in-surface direction in the film surface. Atthis time, because the ferromagnetic layer 24 c is isotropic withrespect to the rotation about the perpendicular axis, the value of φ2 isarbitrary.

Next, the case original in this technology where the strength Δex of themagnetic coupling energy between the magnetizations M1 and M2 differsfrom zero while the magnetizations M1 and M2 are coupled with each otherand moved is considered. According to the definition, when the strengthΔex is positive, the directions of the magnetizations M1 and M2 aremoved to be parallel. This is sometimes called ferromagnetic coupling.In contrast, when the strength Δex is negative, the directions of themagnetizations M1 and M2 are moved to be antiparallel. This is sometimescalled anti-ferromagnetic coupling. To simplify the descriptionhereinafter, although only the case where the strength Δex is positiveis considered, the same discussion can be performed in the case wherethe strength Δex is negative.

When the differences Δ1 and Δ2 are positive together, the directions ofthe magnetizations M1 and M1 in the equilibrium state become parallel tothe perpendicular axis regardless of the strength Δex. This is the sameas in the storage element 3 shown in FIG. 4, and the increase of thereversal time may be unavoidable. In contrast, when the differences Δ1and Δ2 are negative together, the magnetizations M1 and M1 in theequilibrium state are respectively directed to in-surface directions inthe film surfaces regardless of the strength Δex. At this time,regardless of the value of φ1, the relative angle between the directionof the magnetization M22 of the magnetization fixed layer 22 and thedirection of the magnetization M1 of the ferromagnetic layer 24 abecomes constantly 90 degrees. Therefore, no change in resistance due tothe magnetoresistive effect is caused, and no information may be readout. In this case, a storage element in which the signs of thedifferences Δ1 and Δ2 are the same may not be used as a storage elementcomposing the ST-MRAM. As described above, the signs of the differencesΔ1 and Δ2 in the storage element 20 according to the embodiment of thepresent technology should be differentiated from each other.

As described above, when the signs of the differences Δ1 and Δ2 differfrom each other, the easy magnetization axis of the magnetization of oneferromagnetic layer is perpendicular to the film surface while the easymagnetization axis of the magnetization of the other ferromagnetic layeris placed in the film surface.

These two magnetizations of which the directions conflict with eachother may be inclined with respect to the perpendicular direction due tothe coupling at the energy strength Δex. The energy strength Δex has anupper limit. Assuming that the strength Δex is infinitely large, themagnetizations M1 and M2 should be parallel to each other. In this case,according to magnitude correlation between the differences Δ1 and Δ2,the total of the easy magnetization axes becomes directed to beperpendicular to the film surface or to be placed in the film surface.Even though the strength Δex is not infinitely large, when the strengthΔex is larger than a certain strength, the magnetizations M1 and M2undesirably become parallel to each other.

Therefore, to determine the upper limit of the strength Δex, theinventors of the present technology calculated the upper limit Δexmax,at which the magnetizations M1 and M2 become parallel to each other, inthe case of various combinations of the differences Δ1 and Δ2 by usingthe Equation 2. An example is shown in FIG. 7. In FIG. 7, the differenceΔ2 is fixed to −40, and the difference Δ1 is changed in the range from 0to 100. White circles indicate upper limits of the strength Δexdetermined by the calculation. When the strength Δex is smaller than thecorresponding upper limit, the magnetizations M1 and M2 may be inclinedtogether with respect to the perpendicular direction. The dependency ofthe limit Δexmax on the difference Δ1 in the case of the value Δ1+Δ2being smaller than zero differs from the dependency in the case of thevalue Δ1+Δ2 being larger than zero. A curved line C41 indicates the Δ1dependency of the strength Δexmax when the value Δ1+Δ2 is smaller thanzero. In contrast, a curved line C42 indicates the Δ1 dependency of thestrength Δexmax when the value Δ1+Δ2 is larger than zero. The inventorstried to find out an equation adequately expressing these curved lines,and realized that the curved lines C41 and C42 were expressed by thefollowing equation,Δexmax=abs(2×Δ1×Δ2(Δ1+Δ2))

Here, abs denotes a function for changing to an absolute value. Now,only the case where the strength Δex is positive is considered in thisequation. However, in the same manner, the equation is obtained in thecase where the strength Δex is negative. As a result, the condition thatthe magnetizations M1 and M2 are inclined together with respect to theperpendicular direction is as follows.abs(Δex)<abs(2×Δ1×Δ2/(Δ1+Δ2))

As described above, in the present technology, the condition that themagnetizations M1 and M2 are inclined together with respect to theperpendicular direction is found out. When the differences Δ1 and Δ2 andthe strength Δex satisfying this condition are given, the equivalentstate in which the magnetizations M1 and M2 are inclined with respect tothe perpendicular axis is obtained. Then, the value obtained bysubtracting the value of the magnetic energy in the equivalent statefrom the value of the magnetic energy indicated by the Equation 2denotes the excitation energy E of the storage element 20 according tothe embodiment of the present technology. Further, the excitation energyE necessary to reverse the directions of the magnetizations M1 and M2 isthe index Δ of the thermal stability. Therefore, when the differences Δ1and Δ2 and the strength Δex are given, the excitation energy E and theindex Δ of the thermal stability are uniquely determined.

The dependency of the index Δ of the thermal stability on the strengthΔex is shown n FIG. 8. In FIG. 8, the relation Δ1>0>Δ2 is satisfied.However, the relation Δ2>0>Δ1 is also allowed. In this case, thedifferences Δ1 and Δ2 in FIG. 8 are changed with each other. When thestrength Δex is zero, the index Δ is equal to the difference Δ1.Although the index Δ is decreased with the increase of the strength Δex,the dependency in the case of the value Δ1+Δ2 being smaller than zerodiffers from the dependency in the case of the value Δ1+Δ2 being largerthan zero. A curved line C51 corresponds to the value Δ1+Δ2 beingsmaller than zero, while a curved line C52 corresponds to the valueΔ1+Δ2 being larger than zero. When the value Δ1+Δ2 is smaller than zero,the difference Δ is converged to zero while the strength Δex approachesthe limit Δexmax. In contrast, when the value Δ1+Δ2 is larger than zero,the index Δ is converged to the value Δ1+Δ2 while the strength Δexapproaches the limit Δexmax.

The index Δ of thermal stability denotes an index indicating toleranceto the thermal fluctuation of the storage element 20. When the storageelement 20 is used as a nonvolatile memory, it is necessary to holdinformation in a guaranteed operation period of time. This means thatthe index Δ of thermal stability should be higher than a certainconstant value. Although the lower limit of the index Δ changes with thememory capacity and the guaranteed operation period of time, the lowerlimit is approximately within a range from 40 to 70. As the index Δ isincreased, tolerance to heat is strengthened. However, because energynecessary for writing is also increased, it is not necessary tounnecessarily increasing the index Δ.

Now, the design value of the index Δ of thermal stability is indicatedby Δ0. In this case, according to FIG. 8, the condition that the indexΔ=Δ0 is obtained by adjusting the strength Δex is to satisfy therelation Δ1+Δ2<Δ0<Δ1. FIG. 8 shows the case of the relation Δ1>0>Δ2.However, when the case of the relation Δ2>0>Δ1 is also considered, thecondition that the differences Δ1 and Δ2 should be satisfied is therelation Δ1+Δ2<Δ0<max(Δ1, Δ2). Here, max denotes a function forselecting a maximum value from the differences Δ1 and Δ2.

Conditions that the differences Δ1 and Δ2 should be satisfied areplatted in FIG. 9. Here, the design value of the index Δ of thermalstability is indicated by Δ0, A straight line L61 indicates the relationΔ1+Δ2=Δ0, a straight line L62 indicates the difference Δ1=Δ0, and astraight line L63 indicates the difference Δ2=Δ0. A region D64, placedon the lower side of the line L61 and placed on the right side of theline L62, and a region D65, placed on the lower side of the line L61 andplaced on the upper side of the line L63, are a range of the differencesΔ1 and Δ2 satisfying the condition of the relation Δ1+Δ2<Δ0<max(Δ1, Δ2).

When the differences Δ1 and Δ2 are placed together in the region D64 orD65, the strength Δex may be adjusted such that the index Δ of thermalstability becomes equal to the design value Δ0, and the directions ofthe magnetizations M1 and M2 at this time may be inclined with respectto the perpendicular axis. Although the condition that the signs of thedifferences Δ1 and Δ2 should be differentiated from each other has beendescribed hereinbefore, this condition is automatically satisfied whenthe differences Δ1 and Δ2 are placed together in the region D64 or D65.

Next, the simulation about spin injecting magnetization reversal (spintorque transfer) in the case of using the storage element 20 accordingto the embodiment of the present technology is performed, while thesimulation in the case of using the storage element 3 shown in FIG. 4 isperformed for a comparison.

FIG. 10 shows the relation between the excitation energy E and thereversal time ts for a certain current. The excitation energy E of thehorizontal axis is plotted on a logarithm scale. Here, a valuecalculated from a magnetization direction at the time a current isapplied is used as the excitation energy E. The magnetization directionis shifted from the equilibrium state due to thermal fluctuation. Thismeans that this shift becomes large as the excitation energy E isincreased (goes to the right side in FIG. 10).

As described above, the relation between the excitation energy E and thereversal tine ts in the storage element 3 is expressed by theEquation 1. When the magnetization is perfectly set in the equilibriumstate, the infinite reversal time is necessary. However, in the actualcase, because the value of the excitation energy E is equal to or higherthan zero due to thermal fluctuation, the magnetization may be reversedin a finite period of time. This tendency is indicated by a curved lineC71. When the excitation energy E of the horizontal axis is indicated ona logarithm scale, the curved line C71 is approximately a straight line.It will be realized that the magnetization is reversed in a shorter timeas the excitation energy E is increased.

Now, it is assumed that a current application time is 20 nanoseconds. Inthis case, as indicated by a point P73, if the logarithmic value of theexcitation energy E is equal to −20, the reversal just in 20 nanosecondsmay be performed. The excitation energy E is not fixed to a certainconstant value, but always changes due to thermal fluctuation. When thelogarithmic value of the excitation energy E is equal to or higher than−20, the reversal in 20 nanoseconds may be performed. In contrast, whenthe logarithmic value of the excitation energy E is equal to or lowerthan −20, the reversal in 20 nanoseconds may not be performed. That is,a writing error is caused. As described above, in the storage element 3,when the magnetization angle at the time a current is applied ischanged, the period of time necessary for the reversal is changed.Therefore, the writing operation sometimes succeeds and sometimes failsdue to the influence of the change in the reversal time.

In contrast, the relation between the excitation energy E and thereversal time ts in the case of using the storage element 20 accordingto the embodiment of the present technology is indicated by a curvedline C72. This line C72 differs from the curved line C71 for the storageelement 3 shown in FIG. 4, and the line C72 indicates no increase of thereversal time ts even when the excitation energy E is decreased. Thereason is that, because the directions of the magnetizations M1 and M2are inclined with respect to the perpendicular axis even when theexcitation energy E is equal to zero (a negative infinite value on alogarithm scale shown in FIG. 10), a finite spin torque acts on themagnetizations M1 and M2.

In the calculation example indicated by the curved line C72 shown inFIG. 10, when the logarithmic value of the excitation energy E isapproximately equal to or lower than zero, the reversal time ts isconstantly 10 nanoseconds. When the logarithmic value of the excitationenergy E is approximately equal to or higher than zero, the reversaltime ts is further shortened. This means that the reversal time ts doesnot exceed 10 nanoseconds even when the magnetizations M1 and M2 aredirected to any directions at the time a current is applied. Asdescribed above, in the storage element 20 according to the embodimentof the present technology, the upper limit (10 nanoseconds in thecalculation example shown in FIG. 10) of the reversal time ts isdetermined regardless of the directions of the magnetizations M1 and M2set at the time a current is applied. Therefore, when a currentapplication time is set to be equal to or larger than this upper limit,the writing can be performed without causing any writing error.

Here, the physical meaning of the excitation energy E will besupplemented. As described above, the value of the excitation energy Eis finite due to thermal fluctuation, in the case where a storage layeris structured by a single ferromagnetic layer in the same manner as inthe storage element 3 shown in FIG. 4, the probability that theexcitation energy E becomes smaller than a value X is given by1-exp(−X). (When a storage layer is structured by a plurality offerromagnetic layers in the same manner as in the storage element 20according to the embodiment of the present technology, this strictequation may not be given, but the tendency is almost the same.) In thecalculation example shown in FIG. 10, the logarithmic value of theexcitation energy E corresponding to the reversal time ts of 20nanoseconds is −20. Therefore, when the logarithmic value of theexcitation energy E is lower than −20; the writing in a currentapplication time of 20 nanoseconds is failed. The probability that thelogarithmic value of the excitation energy E is lower than −20 iscalculated 1-exp(−exp(−20))≈2×10⁻⁹ by using the equation 1-exp(−X).Therefore, the excitation energy E and the writing error, rate areclosely related to each other, Even when the excitation energy E issmall, it may be important to shorten the reversal time ts for thepurpose of reducing the writing error rate. In consideration of thispoint, the embodiment of the present technology in which the reversaltime ts is placed at a constant value even when the excitation energy Eis small to any degree is appropriate for the purpose of reducing thewriting error rate.

The memory using the storage element 20 shown in FIG. 5 is obtained byreplacing the storage element 3 in the memory shown in FIG. 1, FIG. 2and FIG. 3 with the storage element 20.

As shown in the drawings, in this memory, a large number of first wires(e.g., bit lines) 1 extend perpendicular to a large number of secondwires (e.g., word lines) 6 in a matrix shape, and the storage element 20is located at each of cross-over points of the first sires 1 and thesecond wires 6.

The storage element 20 is formed in a circular shape in a plane, and hasa cross-sectional structure shown in FIG. 5.

Further, as shown in FIG. 5, the storage element 20 has themagnetization fixed layer 22 and the storage layer (the free magnetizedlayer) 24.

Each memory element 20 forms one of memory cells of the memory.

Each of the first wires 1 and the second wires 6 is electricallyconnected with the corresponding storage element 20, so that a currentmay flow through the storage element 20 via these wires 1 and 6 in thelamination direction (the vertical direction) of each layer of thestorage element 20.

Then, when the current flows through the storage element 20, thedirections of the magnetizations of the storage layer 24 are reversed.Therefore, the recording of information may be performed. Morespecifically, in the same manner as in the ST-MRAM shown in FIG. 4, thedirections of the magnetizations of the storage layer 24 are reversed bychanging the polarity of the current (the direction of the current)flowing through the storage element 20, and the recording of informationis performed.

In the embodiment described above, in each storage element 20 composingone memory cell of the memory, the storage layer 24 has a laminatedstructure of the ferromagnetic layer 24 a, the coupling layer 24 b, andthe ferromagnetic layer 24 c. Because of this aminated structure, themagnetization M1 of the ferromagnetic layer 24 a and the magnetizationM2 of the ferromagnetic layer 24 c may have the directions inclined withrespect to the axis perpendicular to the film surfaces. Therefore, thephenomenon that no spin torque acts on the magnetizations M1 and M2 maybe avoided.

That is, the recording of information may be performed by reversing thedirections of the magnetizations M1 and M2 within a predetermined finiteperiod of time.

Accordingly, in this embodiment, because the writing of information maybe performed by reversing the directions of the magnetizations of thestorage layer within a predetermined period of time, the writing errormay be reduced, and the writing operation may be performed in a shortertime. Further, because the writing error may be reduced, the reliabilityin the writing operation may be improved. Moreover, because the winingoperation may be performed in a shorter time, the operation may beperformed at a high speed. That is, the memory having a high reliabilityin the writing operation while being operated at a high speed may beobtained.

In the embodiment described above, the storage layer (the freemagnetized layer) 24 has a three-layer structure of the ferromagneticlayer 24 a, the coupling layer 24 b, and the ferromagnetic layer 24 c.However, in the present technology, a laminated structure having anarbitrary number of layers other than the three-layer structure may beused.

Further, in the embodiment described above, the magnetization fixedlayer (the reference layer) 22, the intermediate layer (the nonmagneticlayer) 23, and the storage layer (the free magnetized layer) 24 arelocated from the lower layer side in that order. However, in the presenttechnology, the arrangement in which these layers are located in thereverse order in the vertical direction may be allowed. When themagnetization fixed layer 22 is located on the lower layer side like theembodiment described above, comparatively thick layers such as anantiferromagnetic layer (not shown) are located on the lower layer side.Therefore, as compared with the structure in which the layer 22 islocated on the upper layer side, it is advantageous that the etching forpatterning the storage element may be easily performed.

The present technology is not limited to only the embodiment describedabove, and may be variously modified without departing from the gist ofthe present technology.

<4. Modification>

The structure of the storage element 3 or the storage element 20according to the embodiment of the present technology is used for amagnetoresistive effect element such as a TMR element. However, themagnetoresistive effect element acting as the TMR element may be appliedto not only the memory described above but also a magnetic head, a harddisc drive quipped with this magnetic head, an integrated circuit chip,a personal computer, a portable terminal, a cellular phone, variouselectronic equipment such as a magnetic sensor device, electronic goods,and the like.

As an example, a magnetoresistive effect element 101, which has thestructure of the storage element 3 or 20 and is applied to a combinedtype magnetic head 100, is shown in FIG. 11A and FIG. 11B. FIG. 11A is aperspective view of the combined type magnetic head 100 with partsbroken away to reveal the inner structure of the head 100, and FIG. 11Bis a cross-sectional view of the combined type magnetic head 100.

The combined type magnetic head 100 is a magnetic head used for a harddisc device and the like. The head 100 has a magnetoresistive effecttype magnetic head, to which the present technology is applied, formedon a substrate 122 and also has an inductive type magnetic head formedso as to be laminated on the magnetoresistive effect type magnetic head.Here, the magnetoresistive effect type magnetic head is operated as ahead for reproduction, and the inductive type magnetic head is operatedas a head for recording. That is, this combined type magnetic head 100has the combination of a head for reproduction and head for recording.

The magnetoresistive effect type magnetic head loaded on the combinedtype magnetic head 100 is a so-called shield type MR head, and has afirst magnetic shield 125 formed on the substrate 122 via an insulatinglayer 123, the magnetoresistive effect element 101 formed on the firstmagnetic shield 125 via the insulating layer 123, and a second magneticshield 127 formed on the magnetoresistive effect element 101 via theinsulating layer 123. The insulating layer 123 is formed of aninsulating material such as Al₂O₃ or SiO₂.

The first magnetic shield 125 magnetically shields the lower layer sideof the magnetoresistive effect element 101 and is formed of a softmagnetic material such as Ni—Fe. On this first magnetic shield 125, themagnetoresistive effect element 101 is formed via the insulating layer123.

The magnetoresistive effect element 101 functions as a magnetic sensingelement that detects a magnetic signal from a magnetic recording medium,in the magnetoresistive effect type magnetic head. This magnetoresistiveeffect element 101 has the same film structure as that of the storageelement 3 or 20 described above.

This magnetoresistive effect element 101 is formed approximately in arectangular shape and has a side surface exposed to a surface facing amagnetic recording medium. On both ends of this magnetoresistive effectelement 101, bias layers 128 and 129 are located. Further, connectingterminals 130 and 131 respectively connected with the bias layers 128and 129 are formed. A sensing current is given to the magnetoresistiveeffect element 101 via the connecting terminals 130 and 131.

Moreover, a second magnetic shield 127 is located on the upper portionof the bias layers 128 and 129 via the insulating layer 123.

The inductive type magnetic head laminated and formed on themagnetoresistive effect type magnetic head has a magnetic core,including the second magnetic shield 127 and an upper layer core 132,and a thinned film coil 133 formed so as to be wound around the magneticcore.

The upper layer core 132 forms a closed magnetic circuit in cooperationwith the second magnetic shield 127 and acts as a magnetic core of thisinductive type magnetic head. The core 132 is formed of a soft magneticmaterial such as Ni—Fe. Here, the second magnetic shield 127 and theupper layer core 132 are formed so as to have front end portions,exposed to the surface facing the magnetic recording medium, and to beadjacent to each other in rear end portions thereof. Here, the front endportions of the second magnetic shield 127 and the upper layer core 132are formed such that the layer 127 and the core 132 are away from eachother by a predetermined gap g on the surface facing the magneticrecording medium. That is, in the combined type magnetic head 100, thesecond magnetic shield 127 magnetically shields the upper layer side ofthe magnetoresistive effect element 101 and also acts as a magnetic coreof the inductive type magnetic head. This magnetic core of the inductivetype magnetic head is formed by the second magnetic shield 127 and theupper layer core 132. The gap g denotes a recording magnetic gap of theinductive type magnetic head.

Further, the thinned film coil 133 buried into the insulating layer 123is formed on the second magnetic shield 127. Here, the thinned film coil133 is formed so as to be wound around the magnetic core composed of thesecond magnetic shield 127 and the upper layer core 132. Both endportions (not shown) of this thinned film coil 133 are exposed to theoutside to form external connecting terminals of the inductive typemagnetic head on both ends of the coil 133. That is, when a magneticsignal is recorded on the magnetic recording medium, a recording currentis given from the external connecting terminals to the thinned film coil133.

The combined type magnetic head 121 as described above is equipped withthe magnetoresistive effect type magnetic head as a head forreproduction, and this magnetoresistive effect type magnetic head hasthe magnetoresistive effect element 101, to which the present technologyis applied, as a magnetic sensing element for detecting a magneticsignal from the magnetic recording medium. Because the magnetoresistiveeffect element 101, to which the present technology is applied, has verysuperior characteristics as described above, this magnetoresistiveeffect type magnetic head may deal with the further heightening of therecording density in the magnetic recording.

The present technique may adopt following structures.

-   -   (1) A storage element comprising: a magnetization fixed layer;        and a magnetization free layer including a plurality of        ferromagnetic layers laminated together with a coupling layer        formed between each pair of adjacent ferromagnetic layers,        wherein magnetization directions of the ferromagnetic layers are        inclined with respect to a magnetization direction of the        magnetization fixed layer.    -   (2) The magnetic storage element according to (1), further        comprising a nonmagnetic intermediate layer formed between the        magnetization fixed layer and the magnetization free layer.    -   (3) The magnetic storage element according to (2), wherein the        intermediate layer is formed of insulating materials and is a        tunnel insulating layer.    -   (4) The magnetic storage element according to (1), wherein a        magnetization direction of the magnetization fixed layer in a        direction perpendicular to a film surface of the magnetization        fixed layer.    -   (5) The magnetic storage element according to (1), further        comprising an underlying layer and an anti-ferromagnetic layer        formed between the underlying layer and the magnetization fixed        layer.    -   (6) The magnetic storage element according to (1), wherein the        magnetization free layer includes a first ferromagnetic layer        and a second ferromagnetic layer with one of the coupling layers        formed therebetween, wherein a perpendicular axis extends in a        direction perpendicular to a film surface of the magnetization        free layer through the magnetization free layer, wherein an        angle between the direction of magnetization of the first        ferromagnetic layer and the perpendicular axis is θ₁, and        wherein an angle between the direction of the magnetization of        the second ferromagnetic layer and the perpendicular axis is        defined as θ₂.    -   (7) The magnetic storage element according to (6), wherein a        reference line passes through a center of the first and second        ferromagnetic layers in a top view, and wherein when the a first        magnetization M1 of the first ferromagnetic layer and a second        magnetization M2 of the second ferromagnetic layer are        respectively projected onto film surfaces of the first and        second ferromagnetic layers, an angle between the direction of        the first magnetization M1 and the reference line is defined as        φ₁, and the angle between the direction of the second        magnetization M2 and the reference line is defined as φ₂.    -   (8) The magnetic storage element according to (7), wherein a        magnetic energy ∈ of the storage layer 24 is expressed by the        following Equation 2:        ∈=Δ₁ sin²θ₁+Δ₂ sin²θ₂−Δ_(ex)(cos θ₁ cos θ₂+sin θ₁ sin₂        cos(φ₁−φ₂)),        wherein a first energy difference obtained by subtracting a        strength of the mag energy at the time the first magnetization        M1 is directed to the perpendicular direction (θ₁=0 degree) from        a strength of the magnetic energy at the time the first        magnetization M1 is directed to an in-surface direction (θ₁=90        degrees) is indicated by Δ₁, wherein a second energy difference        obtained by subtracting a strength of the magnetic energy at the        time the second magnetization M2 is directed to the        perpendicular direction (θ₂=0 degree) from a strength of the        magnetic energy at the time the second magnetization M2 is        directed to an in-surface direction (θ₂=90 degrees) is indicated        by Δ₂, and wherein a strength of the magnetic coupling energy        between the fist magnetization M1 and the second magnetization        M2 is indicated by Δ_(ex.)    -   (9) The magnetic storage element according to (8), wherein one        of the following conditions apply: (a) if a first energy        difference Δ₁ is positive, the second energy difference Δ₂ is        negative; and (b) if a first energy difference Δ₁ is negative,        the second energy difference Δ₂ is positive.    -   (10) The magnetic storage element according to (8), wherein the        following condition is satisfied:        abs(Δ_(ex))<abs(2×Δ₁×Δ₂/(Δ₁+Δ₂)).    -   (11) The magnetic storage element according to (1), wherein the        magnetization free layer includes a first ferromagnetic layer        having a first magnetization M1, a second ferromagnetic layer        having a second magnetization M2, and one of the coupling layers        formed therebetween, and wherein a first magnetization direction        of the first ferromagnetic layer is inclined with respect o a        second magnetization direction of the second ferromagnetic        layer.

The present technique may also adopt following structures.

-   -   (12) A method of writing information to a storage element        including a magnetization fixed layer, and a magnetization free        layer including a plurality of ferromagnetic layers laminated        together with a coupling layer formed between each pair of        adjacent ferromagnetic layers, the method comprising: applying a        current in a magnetization direction of the magnetization fixed        layer to cause a spin torque magnetization reversal in the        magnetization free layer, wherein magnetization directions of        the ferromagnetic layers are inclined with respect to the        magnetization direction of the magnetization fixed layer.    -   (13) The method according to (12), wherein the storage element        further includes a nonmagnetic intermediate layer formed between        the magnetization fixed layer and the magnetization free layer.    -   (14) The method according to (13), wherein the intermediate        layer is formed of insulating materials and is a tunnel        insulating layer.    -   (15) The method according to (12), wherein a magnetization        direction of the magnetization fixed layer is in a direction        perpendicular to a film surface of the magnetization fixed        layer.    -   (16) The method according to (12), further comprising an        underlying layer and an anti-ferromagnetic layer formed between        the underlying layer and the magnetization fixed layer.    -   (17) The method according to (12), wherein the magnetization        free layer includes a first ferromagnetic layer and a second        ferromagnetic layer with one of the coupling layers formed        therebetween, wherein a perpendicular axis extends in a        direction perpendicular to a film surface of the magnetization        free layer through the magnetization free layer, wherein an        angle between the direction of magnetization of the first        ferromagnetic layer and the perpendicular axis is θ₁, and        wherein an angle between the direction of the magnetization of        the second ferromagnetic layer and the perpendicular axis is        defined as θ₂.    -   (18) The method according to (17), wherein a reference line        passes through a center of the first and second ferromagnetic        layers in a top view, and wherein when the a first magnetization        M1 of the first ferromagnetic layer and a second magnetization        M2 of the second ferromagnetic layer are respectively projected        onto film surfaces of the first and second ferromagnetic layers,        an angle between the direction of the first magnetization M1 and        the reference line is defined as φ₁, and the angle between the        direction of the second magnetization M2 and the reference line        is defined as θ₂.    -   (19) The method according to (18), wherein a magnetic energy ∈        of the storage layer 24 is expressed by the following Equation        2:        ∈=Δ₁ sin²θ₁+Δ₂ sin³θ₂−Δ_(ex)(cos θ₁ cos θ₂+sin θ₁ sin θ₂        cos(φ₁−φ₂)),        wherein a first energy difference obtained by subtracting a        strength of the magnetic energy at the time the first        magnetization M1 is directed to the perpendicular direction        (θ₁=0 degree) from a strength of the magnetic energy at the time        the first magnetization M1 is directed to an in-surface        direction (θ₁=90 degrees) is indicated by Δ₁, wherein a second        energy difference obtained by subtracting a strength of the        magnetic energy at the time the second magnetization M2 is        directed to the perpendicular direction (θ₂=0 degree) from a        strength of the magnetic energy at the time the second        magnetization M2 is directed to an in-surface direction (θ₂=90        degrees) is indicated by Δ₂, and wherein a strength of the        magnetic coupling energy between the fist magnetization M1 and        the second magnetization M2 is indicated by Δ_(ex.)    -   (20) The method according to (19), wherein one of the following        conditions apply: (a) if a first energy difference Δ₁ is        positive, the second energy difference Δ₂ is negative; and (b)        if a first energy difference Δ1 is negative, the second energy        difference Δ2 is positive.    -   (21) The method according to (19), wherein the following        condition is satisfied: abs(Δ_(ex))<abs(2×Δ₁×Δ₂/(Δ₁+Δ₂)).    -   (22) The method according to (12), wherein the magnetization        free layer includes a first ferromagnetic layer having a first        magnetization M1 and a second ferromagnetic layer having a        second magnetization M2, and one of the coupling layers formed        therebetween, and wherein a first magnetization direction of the        first ferromagnetic layer is inclined with respect to a second        magnetization direction of the second ferromagnetic layer.

The present technique may also adopt following structures.

-   -   (23) A spin torque magnetic random access memory element        comprising: a magnetization fixed layer having a fixed        magnetization in a perpendicular direction relative to a film        surface of the magnetization fixed layer; a magnetization free        layer including a plurality of ferromagnetic layers laminated        together with a coupling layer formed between each pair of        adjacent ferromagnetic layers, thereby magnetically coupling the        ferromagnetic layers; and a nonmagnetic layer formed between the        magnetization fixed layer and the magnetization free layer,        wherein magnetization directions of the ferromagnetic layers are        inclined with respect to the perpendicular direction.    -   (24) The spin torque magnetic random access memory element        according to (23), wherein the nonmagnetic layer is formed of        insulating materials and is a tunnel insulating layer.    -   (25) The spin torque magnetic random access memory element        according to (24), wherein a magnetization direction of the        magnetization fixed layer is in a direction perpendicular to a        film surface of the magnetization fixed layer.    -   (26) The spin torque magnetic random access memory element        according to (23), further comprising an underlying layer and an        anti-ferromagnetic layer formed between the underlying layer and        the magnetization fixed layer.    -   (27) The spin torque magnetic random access memory element        according to (23), wherein the magnetization free layer includes        a first ferromagnetic layer and a second ferromagnetic layer        with one of the coupling layers formed therebetween, wherein a        perpendicular axis extends in a direction perpendicular to a        film surface of the magnetization free layer through the        magnetization free layer, wherein an angle between the direction        of magnetization of the first ferromagnetic layer and the        perpendicular axis is θ₁, and wherein an angle between the        direction of the magnetization of the second ferromagnetic layer        and the perpendicular axis is defined as θ₂.    -   (28) The spin torque magnetic random access memory element        according to (27), wherein a reference line passes through a        center of the first and second ferromagnetic layers in a top        view, and wherein when the a first magnetization M1 of the first        ferromagnetic layer and a second magnetization M2 of the second        ferromagnetic layer are respectively projected onto film        surfaces of the first acrd second ferromagnetic layers, an angle        between the direction of the first magnetization M1 and the        reference line is defined as φ₁, and the angle between the        direction of the second magnetization M2 and the reference line        is defined as φ₂.    -   (29) The spin torque magnetic random access memory element        according to (28), wherein a magnetic energy ∈ of the storage        layer 24 is expressed by the following Equation 2:        ∈=Δ₁ sin²θ₁+Δ₂ sin²θ₂−Δ_(ex)(cos θ₁ cos θ₂+sin θ₁ sin θ₂        cos(φ₁−φ₂))        wherein a first energy difference obtained by subtracting a        strength of the magnetic energy at the time the first        magnetization M1 is directed to the perpendicular direction        (θ₁=0 degree) from a strength of the magnetic energy at the time        the first magnetization M1 is directed to an in-surface        direction (θ₁=90 degrees) is indicated by Δ₁, wherein a second        energy difference obtained by subtracting a strength of the        magnetic energy at the time the second magnetization M2 is        directed to the perpendicular direction (θ₂=0 degree) from a        strength of the magnetic energy at the time the second        magnetization M2 is directed to an in-surface direction (θ₂=90        degrees) is indicated by Δ₂, and wherein a strength of the        magnetic coupling energy between the fist magnetization M1 and        the second magnetization M2 is indicated by Δ_(ex).    -   (30) The spin torque magnetic random access memory element        according to (23), wherein one of the following conditions        apply: (a) if a first energy difference Δ₁ is positive, the        second energy difference Δ₂ is negative; and (b) if a first        energy difference Δ1 is negative, the second energy difference        Δ2, is positive.    -   (31) The spin torque magnetic random access memory element        according to (29), wherein the following condition is satisfied:        abs(Δ_(ex))<bs(2×Δ₁×Δ₂/(Δ₁+Δ₂)).    -   (32) The spin torque magnetic random access memory element        according to (23), wherein the magnetization free layer includes        a first ferromagnetic layer having a first magnetization M1, a        second ferromagnetic layer having a second magnetization M2, and        one of the coupling layers formed therebetween, and wherein a        first magnetization direction of the first ferromagnetic layer        is inclined with respect to a second magnetization direction of        the second ferromagnetic layer.

The present technique may also adopt following structures.

-   -   (33) A magnetoresistive effect type magnetic head comprising: a        first magnetic shield formed on a substrate via an insulating        layer; a magnetic sensing element including a magnetization        fixed layer, and a magnetization free layer including a        plurality of ferromagnetic layers laminated together with a        coupling layer formed between each pair of adjacent        ferromagnetic layers; and a secont, magnetic shield formed on        the magnetic sensing element via the insulating layer, wherein        magnetization directions of the ferromagnetic layers are        inclined with respect to a magnetization direction of the        magnetization fixed layer.    -   (34) The magnetoresistive effect type magnetic head according to        (33), wherein the magnetic sensing element is formed in an        approximate rectangular shape and has a side surface exposed to        a surface facing a magnetic recording medium.    -   (35) The magnetoresistive effect type magnetic head according to        (33), further comprising bias layers formed on both ends of the        magnetic sensing element.    -   (36) The magnetoresistive effect type magnetic head according to        (35), further comprising connecting terminals respectively        connected with the bias layers, and the connecting terminals are        configured to transmit a sensing current to the magnetic sensing        element.

The present technique may also adopt following structures.

-   -   (1) A storage element, having a layer structure including: a        storage layer in which a direction of a magnetization is changed        according to information; an intermediate layer being a        nonmagnetic substance; and a magnetization fixed layer, located        on the storage layer via the intermediate layer, in which a        direction of a magnetization is fixed, in which the storage        layer is configured to laminate at least two ferromagnetic        layers on each other via a coupling layer, the two ferromagnetic        layers being magnetically coupled with each other via the        coupling layer, directions of magnetizations of the two        ferromagnetic layers being inclined with respect to a direction        perpendicular to film surfaces of the ferromagnetic layers, and        a magnetized state of the recording layer is changed by a        current flowing in a lamination direction of the layer structure        to perform recording of the information on the storage layer.    -   (2) The storage element according to (1), in which one of the        ferromagnetic layers is configured to have magnetic energy of a        value which is obtained by subtracting a value of the magnetic        energy of the ferromagnetic layer, in which the direction of the        magnetization is perpendicular to a film surface of the        ferromagnetic layer, from a value of the magnetic energy of the        ferromagnetic layer in which the magnetization is directed to an        in-surface direction in the film surface, the other        ferromagnetic layer is configured to have magnetic energy of a        value which is obtained by subtracting a value of the magnetic        energy of the other ferromagnetic layer, in which the direction        of the magnetization is perpendicular to a film surface of the        other ferromagnetic layer, from a value of the magnetic energy        of the other ferromagnetic layer in which the magnetization is        directed to an surface direction in the film surface of the        other ferromagnetic layer, and signs of the values in the        magnetic energy of the ferromagnetic layers are differentiated        from each other.    -   (3) The storage element according to (2), in which the two        ferromagnetic layers are magnetically coupled with each other        via the coupling layer at magnetic energy of a predetermined        value, and an absolute value of the predetermined value of the        magnetic energy is lower than an absolute value of a value which        is obtained by doubling a value obtained by dividing a product        of the value of the magnetic energy of one of the ferromagnetic        layers and the value of the magnetic energy of the other        ferromagnetic layer by a sum of the value of the magnetic energy        of one of the ferromagnetic layers and the value of the magnetic        energy of the other ferromagnetic layer.    -   (4) The storage element according to (2) or (3), in which a        value of an index of thermal stability is set between a value,        which is obtained by adding the vale of the magnetic energy of        one of the ferromagnetic layers to the value of the magnetic        energy of the other ferromagnetic layer, and a maximum value        between the value of the magnetic energy of one of the        ferromagnetic layers and the value of the magnetic energy of the        other ferromagnetic layer.    -   (5) The storage element according to any one of (2) to (4), in        which the value of the index of thermal stability is equal to or        higher than forty.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

REFERENCE SIGNS LIST

-   1 gate electrode-   7 element separating layer-   3, 20 storage element-   4 contact layer-   6 bit lines-   7 source region-   8 drain region-   9 wires-   10 semiconductor substrate-   11, 21 underlayer-   12, 22 magnetization fixed layer-   13, 23 intermediate layer-   14, 24 storage layer-   15, 25 cap layer-   100 combined type magnetic head-   122 substrate-   123 insulating layer-   125 first magnetic shield-   127 second magnetic shield-   128, 129 bias layers-   130, 131 connecting terminals-   132 upper core-   133 thinned film coil

The invention claimed is:
 1. A storage element comprising: amagnetization fixed layer; a magnetization free layer including aplurality of ferromagnetic layers laminated together with a couplinglayer formed between each pair of adjacent ferromagnetic layers; and anonmagnetic intermediate layer that is a tunnel insulating layer and isformed between the magnetization fixed layer and the magnetization freelayer, wherein magnetization directions of the ferromagnetic layers areinclined with respect to a magnetization direction of the magnetizationfixed layer.
 2. The magnetic storage element according to claim 1,wherein a magnetization direction of the magnetization fixed layer is ina direction perpendicular to a film surface of the magnetization fixedlayer.
 3. The magnetic storage element according to claim 1, furthercomprising an underlying layer and an anti-ferromagnetic layer formedbetween the underlying layer and the magnetization fixed layer.
 4. Themagnetic storage element according to claim 1, wherein the magnetizationfree layer includes a first ferromagnetic layer and a secondferromagnetic layer with one of the coupling layers formed therebetween,wherein a perpendicular axis extends in a direction perpendicular to afilm surface of the magnetization free layer through the magnetizationfree layer, wherein an angle between the direction of magnetization ofthe first ferromagnetic layer and the perpendicular axis is θ₁, andwherein an angle between the direction of the magnetization of thesecond ferromagnetic layer and the perpendicular axis is defined as θ₂.5. The magnetic storage element according to claim 4, wherein areference line passes through a center of the first and secondferromagnetic layers in a top view, and wherein when a firstmagnetization M1 of the first ferromagnetic layer and a secondmagnetization M2 of the second ferromagnetic layer are respectivelyprojected onto film surfaces of the first and second ferromagneticlayers, an angle between the direction of the first magnetization M1 andthe reference line is defined as φ₁, and the angle between the directionof the second magnetization M2 and the reference line is defined as φ₂.6. The magnetic storage element according to claim 5, wherein a magneticenergy ε of the storage layer 24 is expressed by the following Equation2:∈=Δ₁ sin²θ₁+Δ₂ sin²θ₂−Δ_(ex)(cos θ₁ cos θ₂+sin θ₁ sin θ₂ cos(φ₁−φ₂))wherein a first energy difference obtained by subtracting a strength ofthe magnetic energy at the time the first magnetization M1 is directedto the perpendicular direction (θ₁=0 degree) from a strength of themagnetic energy at the time the first magnetization M1 is directed to anin-surface direction (θ₁=90 degrees) is indicated by Δ₁, wherein asecond energy difference obtained by subtracting a strength of themagnetic energy at the time the second magnetization M2 is directed tothe perpendicular direction (θ₂=0 degree) from a strength of themagnetic energy at the time the second magnetization M2 is directed toan in-surface direction (θ₂=90 degrees) is indicated by Δ₂, and whereina strength of the magnetic coupling energy between the fistmagnetization M1 and the second magnetization M2 is indicated by Δ_(ex).7. The magnetic storage element according to claim 6, wherein one of thefollowing conditions apply: (a) if a first energy difference Δ₁ ispositive, the second energy difference Δ₂ is negative; and (b) if afirst energy difference Δ₁ is negative, the second energy difference Δ₂is positive.
 8. The magnetic storage element according to claim 6,wherein the following condition is satisfied:abs(Δ_(ex))<abs(2xΔ₁xΔ₂/(Δ₁+Δ₂)).
 9. The magnetic storage elementaccording to claim 1, wherein the magnetization free layer includes afirst ferromagnetic layer having a first magnetization M1, a secondferromagnetic layer having a second magnetization M2, and one of thecoupling layers formed therebetween, and wherein a first magnetizationdirection of the first ferromagnetic layer is inclined with respect to asecond magnetization direction of the second ferromagnetic layer.
 10. Amethod of writing information to a storage element including amagnetization fixed layer, a magnetization free layer including aplurality of ferromagnetic layers laminated together with a couplinglayer formed between each pair of adjacent ferromagnetic layers, and anonmagnetic intermediate layer that is a tunnel insulating layer and isformed between the magnetization fixed layer and the magnetization freelayer, the method comprising: applying a current in a magnetizationdirection of the magnetization fixed layer to cause a spin torquemagnetization reversal in the magnetization free layer, whereinmagnetization directions of the ferromagnetic layers are inclined withrespect to the magnetization direction of the magnetization fixed layer.11. The method according to claim 10, wherein a magnetization directionof the magnetization fixed layer is in a direction perpendicular to afilm surface of the magnetization fixed layer.
 12. The method accordingto claim 10, wherein the magnetization free layer includes a firstferromagnetic layer having a first magnetization M1 and a secondferromagnetic layer having a second magnetization M2, and one of thecoupling layers formed therebetween, and wherein a first magnetizationdirection of the first ferromagnetic layer is inclined with respect to asecond magnetization direction of the second ferromagnetic layer.
 13. Aspin torque magnetic random access memory element comprising: amagnetization fixed layer having a fixed magnetization in aperpendicular direction relative to a film surface of the magnetizationfixed layer; a magnetization free layer including a plurality offerromagnetic layers laminated together with a coupling layer formedbetween each pair of adjacent ferromagnetic layers, thereby magneticallycoupling the ferromagnetic layers; and a nonmagnetic layer that is atunnel insulating layer and is formed between the magnetization fixedlayer and the magnetization free layer, wherein magnetization directionsof the ferromagnetic layers are inclined with respect to theperpendicular direction.
 14. The spin torque magnetic random accessmemory element according to claim 13, wherein a magnetization directionof the magnetization fixed layer is in a direction perpendicular to afilm surface of the magnetization fixed layer.
 15. The spin torquemagnetic random access memory element according to claim 13, furthercomprising an underlying layer and an anti-ferromagnetic layer formedbetween the underlying layer and the magnetization fixed layer.
 16. Thespin torque magnetic random access memory element according to claim 13,wherein the magnetization free layer includes a first ferromagneticlayer having a first magnetization M1, a second ferromagnetic layerhaving a second magnetization M2, and one of the coupling layers formedtherebetween, and wherein a first magnetization direction of the firstferromagnetic layer is inclined with respect to a second magnetizationdirection of the second ferromagnetic layer.
 17. A magnetoresistiveeffect type magnetic head comprising: a first magnetic shield formed ona substrate via an insulating layer; a magnetic sensing elementincluding a magnetization fixed layer, a magnetization free layerincluding a plurality of ferromagnetic layers laminated together with acoupling layer formed between each pair of adjacent ferromagneticlayers, and a nonmagnetic intermediate layer that is a tunnel insulatinglayer and is formed between the magnetization fixed layer and themagnetization free layer; and a second magnetic shield formed on themagnetic sensing element via the insulating layer, wherein magnetizationdirections of the ferromagnetic layers are inclined with respect to amagnetization direction of the magnetization fixed layer.
 18. Themagnetoresistive effect type magnetic head according to claim 17,wherein the magnetic sensing element is formed in an approximaterectangular shape and has a side surface exposed to a surface facing amagnetic recording medium.
 19. A storage element comprising: amagnetization fixed layer; and a magnetization free layer including aplurality of ferromagnetic layers laminated together with a couplinglayer formed between each pair of adjacent ferromagnetic layers, whereinmagnetization directions of the ferromagnetic layers are inclined withrespect to a magnetization direction of the magnetization fixed layer,the magnetization direction of the magnetization fixed layer being in adirection perpendicular to a film surface of the magnetization fixedlayer.
 20. A storage element comprising: a magnetization fixed layer;and a magnetization free layer including first and second ferromagneticlayers laminated together with a coupling layer formed therebetween,wherein a magnetization direction of the fixed layer is perpendicular toa film surface of the fixed layer, and magnetization directions of thefirst and second ferromagnetic layers are inclined with respect to themagnetization direction of the magnetization fixed layer, wherein themagnetization free layer includes a first ferromagnetic layer and asecond ferromagnetic layer with one of the coupling layers formedtherebetween, wherein a perpendicular axis extends in a directionperpendicular to a film surface of the magnetization free layer throughthe magnetization free layer, wherein an angle between the direction ofmagnetization of the first ferromagnetic layer and the perpendicularaxis is θ₁, and wherein an angle between the direction of themagnetization of the second ferromagnetic layer and the perpendicularaxis is defined as θ₂.
 21. The storage element according to claim 20,wherein the magnetization directions of the first and secondferromagnetic layers are inclined with respect to one another.